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The case for the Ediacaran fossil roots to the Metazoan Tree

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Abstract

The first challenge to the traditional interpretation of the Late Proterozoic Ediacara fossils came with a paper by A. Seilacher (1984, 1989) which not only proposed that Ediacaran organisms became extinct before the Cambrian, but that they represented a previously unrecognized kingdom of structurally unique multicellular organisms: the Vendozoa. This new model is based on a number of uncontested generalizations about size, shape, lifestyle and preservation, that have persisted in the literature. Many of these assumptions are now shown to be misconceptions, as a consequence of newly discovered material in Australia, Canada and the USSR, revealing a more diverse fossil assemblage and suggesting that the organisms were dominantly benthic. The interpretation of this biota in phylogenetic terms, is vindicated by the realization of strong links between some Ediacaran and Cambrian organisms. -from Author
... In the framework of the 'annelid' hypothesis, only clear anteroposterior asymmetry and visible body segmentation can be considered such evidence. Other described features and structures that could indicate the complexity of the Dickinsonia body plan, such as dorsoventral polarization of the body, intestinal tract, prostomium, intestinal caeca or folds of muscle contractions (Glaessner & Wade, 1966;Wade, 1972;Gehling, 1991;Jenkins, 1992;Dzik, 2000) were not well documented and were hardly taken into account in subsequent studies. A displacement of the right and left halves of the 'segments' along the longitudinal axis of the body of Dickinsonia is often observed on the imprints. ...
... The movement intermittency and the ability of Dickinsonia to push its body through unconsolidated sediment may serve as a new argument in favour of the assumption that these animals had musculature. Previously, this assumption was made after an analysis of compression wrinkles, sometimes observed on the imprints, and extended chains of feeding traces formed by Dickinsonia (Gehling, 1991;Gehling et al. 2005;Evans et al. 2019a). However, this musculature was apparently rather weak and, with the thickness of the burial sediment of > 15 cm, even relatively large specimens of Dickinsonia lost the opportunity to free themselves and escape to the surface. ...
Article
The classical genus of Ediacaran macroorganisms, Dickinsonia, was part of an extensive benthic marine community inhabiting the fields of microbial mats. The remains of Dickinsonia are commonly preserved in the position of adhesion to the habitat substrate. However, these were mobile organisms. In addition to the already known feeding traces of Dickinsonia, structures described as traces of motor activity are reported. Long parallel furrows, extending from the posterior end of the body imprint, are interpreted as imprints of ridges left by an organism moving along the surface of the substrate. Groups of differently shaped grooves laying in the depression that enhalo the Dickinsonia body imprints or accompany their individual areas are interpreted as imprints of ridges and cords of mucous material. They are considered to represent structures of self-determined stretching and lift-off of the body margins from the sub-strate. The rings and arcs of silt-and sand-sized mineral particles bordering the body imprints are composed of material that was supposedly brushed off from the surface of the microbial mat by Dickinsonia. They are considered traces of the adhesion of these organisms to the substrate. Accumulations of multidirectional pulling and tear-off structures, lacking the body imprint but accompanied by the joint plane passing into the overlying sediment and cutting through the bedding, are interpreted as escape traces. The dual modality of the behaviour (attachment and mobility) could indicate the adaptability of Dickinsonia to life in extremely shallow-water environments.
... Glaessner and Wade (1966) put forward an assignment to the Octocorallia (Anthozoa), but were reluctant to support the Pteridiniidae (Family) assignment, given the fragmentary nature of the material. Gehling (1991) suggested that, due to the major morphological differences between Pteridinium and other fronds, it was unlikely to be closely related to them, and instead proposed they could represent macrophytic algae or even members of the Vendozoa (later Vendobionta ;Seilacher 1992;Buss and Seilacher 1994), an idea that was supported by Grazhdankin and Seilacher (2002). Fedonkin (1990), Ivantsov and Fedonkin (2002), and Fedonkin and Ivantsov (2007) argued that the three-vaned architecture of Pteridinium meant it was best considered as a member of the "Trilobozoa" (together with other threefold Ediacaran taxa such as Tribrachidium and Anfesta). ...
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Pteridinium simplex is an iconic erniettomorph taxon best known from late Ediacaran successions in South Australia, Russia, and Namibia. Despite nearly 100 years of study, there remain fundamental questions surrounding the paleobiology and paleoecology of this organism, including its life position relative to the sediment–water interface, and how it fed and functioned within benthic communities. Here, we combine a redescription of specimens housed at the Senckenberg Forschungsinstitut und Naturmuseum Frankfurt with field observations of fossiliferous surfaces, to constrain the life habit of Pteridinium and gain insights into the character of benthic ecosystems shortly before the beginning of the Cambrian. We present paleontological and sedimentological evidence suggesting that Pteridinium was semi-infaunal and lived gregariously in aggregated communities, preferentially adopting an orientation with the long axis perpendicular to the prevailing current direction. Using computational fluid dynamics simulations, we demonstrate that this life habit could plausibly have led to suspended food particles settling within the organism's central cavity. This supports interpretation of Pteridinium as a macroscopic suspension feeder that functioned similarly to the coeval erniettomorph Ernietta , emblematic of a broader paleoecological shift toward benthic suspension-feeding strategies over the course of the latest Ediacaran. Finally, we discuss how this new reconstruction of Pteridinium provides information concerning its potential relationships with extant animal groups and state a case for reconstructing Pteridinium as a colonial metazoan.
... While some species previously described as Charniodiscus are currently considered to be arboreomorphs (e.g., Arborea) (Laflamme et al., 2018;Dunn et al., 2019), those works have not addressed the morphology and taphonomy of the type species of the genus directly. Charniodiscus has been reported to have a worldwide distribution from sites in: Charnwood Forest, UK (e.g., Ford, 1958;Ford, 1962;Ford, 1963;Wilby et al., 2011); South Australia (e.g., Glaessner and Daily, 1959;Glaessner and Wade, 1966;Jenkins and Gehling, 1978;Gehling, 1991;Jenkins, 1992-though most of these occurrences are now considered to be Arborea); the White Sea region of Russia (Fedonkin, 1985;Ivantsov, 2016); north-western Canada (Narbonne and Hofmann, 1987); and Newfoundland, Canada (e.g., Jenkins, 1992;Seilacher, 1992;Hofmann et al., 2008). Charniodiscus is thus a cosmopolitan taxon whose taxonomy and relationship to the somewhat similar Arborea is of global relevance. ...
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Charniodiscus is one of the most iconic and first described of the Ediacaran frondose taxa. Since the diagnosis of the holotype of C. concentricus in 1958, the scarcity and poor preservation of unequivocal specimens has resulted in genus-level taxonomic uncertainty. Since the recent reinterpretation of C. concentricus as a multifoliate frond, other Charniodiscus species—all of which are bifoliate—have been left in taxonomic limbo, with most authors comparing them to the clade Arboreomorpha and also the Rangeomorpha. Reconsideration of the taphonomy of the holotype of C. concentricus has revealed that the frond is bifoliate as first described, and also that the frondose portion was broadly conical rather than planar as previously inferred. The conical frond of Charniodiscus is thus morphologically quite different from all other frondose taxa within the Arboreomorpha. Our emendation of the generic diagnosis of Charniodiscus to encompass bifoliate arboreomorphs with conical fronds without a backing sheet distinguishes Charniodiscus concentricus and C. procerus from more planar leaf-like arboreomorphs such as Arborea, A. longa and A. spinosa, all of which has a distinctive backing sheets. Additionally, we find no evidence of rangeomorph-type fractal branching in Charniodiscus.
... Farmer et al., (1992) reported some low epireliefs Hiemalora specimens from the Stappogiedde Formation in Finnmark, northern Norway but these specimens have a poorly defined central disc surrounded by dense fringes look likes ragged radial appendages. Narbonne, (1994) (Gehling, 1991), Innerelv Member of Finnmark (Farmer et al., 1992) and regionally with Bhander Group of Vindhayn Supergroup (De, 2003), one specimen (Kumar and Pandey, 2009) and two specimens (Parihar, 2019) from the Jodhpur Sandstone of Marwar Supergroup, western Rajasthan, India. ...
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The present study reports and discusses discoidal Ediacaran body fossils identified as Hiemalora stellaris from the Sonia Sandstone of Jodhpur Group, Marwar Supergroup, Western Rajasthan, India. These are preserved as positive relief on the yellowish-brown to pinkish-brown medium to fine-grained sandstone bedding surfaces in Sursagar area. Morphologically, these are circular to sub-circular, mostly flat-discoidal forms or discs surrounded by numerous radiating arms or appendages resembling either to tentacles. Hiemalora is reinterpreted and reconstructed as discoidal hold fast of benthic organism but not found the attached fronds or stem-like structures of the hold fasts in the present materials. The systematic palaeontology, palaeobiology, palaeoenvironment and age of the Hiemalora bearing Ediacaran Sonia Sandstone of Jodhpur Group of Marwar Supergroup have been also discussed.
... However, unequivocal records of anthozoan cnidarians from the critical interval (late Ediacaran to early Cambrian) of animal evolution are extremely rare. Thus, none of the putative Ediacaran hexacorallians 4-6 or octocorallians [7][8][9] has withstood further scrutiny. [10][11][12] Phosphatized polypoid microfossils, including Eolympia pediculata 13 and an undescribed form 14 from basal Cambrian deposits (535 Ma, Fortunian) of South China, have been interpreted as having anthozoan affinities. ...
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Cnidarians diverged very early in animal evolution; therefore, investigations of the morphology and trophic levels of early fossil cnidarians may provide critical insights into the evolution of metazoans and the origin of modern marine food webs. However, there has been a lack of unambiguous anthozoan cnidarians from Ediacaran assemblages, and undoubted anthozoans from the Cambrian radiation of metazoans are very rare and lacking in ecological evidence. Here we report a new polypoid cnidarian, Nailiana elegans gen. et sp. nov., represented by multiple solitary specimens from the early Cambrian Chengjiang biota (∼520 Ma) of South China. These specimens show eight unbranched tentacles surrounding a single opening into the gastric cavity, which may have born multiple mesenteries. Thus, N. elegans displays a level of organization similar to that of extant cnidarians. Phylogenetic analyses place N. elegans in the stem lineage of Anthozoa and suggest that the ancestral anthozoan was a soft-bodied, solitary polyp showing octoradial symmetry. Moreover, one specimen of the new polyp preserves evidence of predation on an epifaunal lingulid brachiopod. This case provides the oldest direct evidence of macrophagous predation, the advent of which may have triggered the emergence of complex trophic/ecological relationships in Cambrian marine communities and spurred the explosive radiation of animal body plans.
... As the most typical structure of MISS, biolaminite was considered as a result of trapping/baffling and binding of sediment grains under microbial mat growth condition where bioturbation is restricted (Gerdes et al., 2000;Bauersachs et al., 2011). Biolaminite is also a common feature of pre-Paleozoic subtidal siliciclastic strata (Gehling, 1991;Kopaska-Merkel and Grannis, 1990;Hagadorn and Bottjer, 1997;Noll and Netto, 2018). ...
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Microbially induced sedimentary structures (MISS) are microbial traces in sandy deposits. They are formed by various modes of microbial behaviour in response to the prevailing physical dynamics in shallow marine environments since the early Archean. The Guojiaba Formation (Cambrian Stage 3), composed of laminated sandstones, siltstones, and mudstones mainly, is characterized by two units of MISS (biolaminite) in the north margin of the Yangtze Block. Biolaminite arises from the microbial growth and it is characterized by alternation of light layers and dark layers in polished slides and the thin sections. The light layers represent the normal background deposition where the development of microbial community is inhibited; whereas, the dark layers are rich in organic materials. SEM identified 7 types of morphologies of microorganisms of a microbenthic community accompanied by a large number of Extracellular Polymeric Substances (EPS) and pyrite framboids from the dark layers. The occurrence of the Biolaminite in the Guojiaba Formation indicates a complex microbial ecosystem within epibenthic microbial mats in a relatively semi-closed to closed sedimentary environment with a high salinity, such as a lagoon, at the summit of the Cambrian Explosion.
... Segmented forms (e.g., Dickinsonia), some of which show polarity and possible cephalization (e.g., Spriggina, Kimberella), provide iconic images of the Ediacara biota. These segmented fossils are commonly regarded as metazoans and likely stem-group bilaterians (Gehling, 1991;Fedonkin and Waggoner, 1997;Sperling and Vinther, 2010;Gold et al., 2015;Evans et al., 2017;Hoekzema et al., 2017;Bobrovskiy et al., 2018). The diverse macroscopic algae and other carbonaceous compressions of the Miaohe assemblage from the Doushantuo Formation of China Ye et al., 2017) are also age-equivalent to the White Sea assemblage, a view supported by the presence of the Miaohe fossil Eoandromeda (Fig. 18.4D) and certain algal fossils in the White Sea assemblage (Xiao et al., 2013;Golubkova et al., 2018). ...
Chapter
The Ediacaran Period (635–538 Ma) has the longest duration among all stratigraphically defined geological periods. The basal boundary of the Ediacaran System is defined by a horizon near the base of the Nuccaleena Formation overlying the Cryogenian diamictite of the Elatina Formation at the Enorama Creek section in South Australia. Most Ediacaran fossils represent soft-bodied organisms and their preservation is affected by taphonomic biases. Thus the Phanerozoic approach of defining stratigraphic boundaries using the first appearance datum of widely distributed, rapidly evolving, easily recognizable, and readily preservable species would have limited success in the Ediacaran System. The subdivision and correlation of the Ediacaran System must therefore be founded on a holistic approach integrating biostratigraphic, chemostratigraphic, paleoclimatic and geochronometric data, particularly carbon and strontium isotopes, glacial diamictites, acanthomorphic acritarchs, Ediacara-type megafossils, and certain tubular fossils. Our preferred scheme is to divide the Ediacaran System into two series separated by the 580 Ma Gaskiers glaciation. Stage-level subdivisions at the bottom and top of the Ediacaran System, including the definition of the second Ediacaran stage (SES) and the terminal Ediacaran stage (TES), are feasible in the near future. Additional Ediacaran stages between the SES and TES can be envisioned, but formal definition of these stages are not possible until various stratigraphic markers are thoroughly tested and calibrated at both regional and global scales.
... The biological affinity of Ediacara-type organisms is still puzzling, but some forms might represent early metazoans (e.g., Fedonkin, 1990;Gehling, 1991;Glaessner, 1984). Furthermore, still little is known about the geobiology of the host ecosystems, that is, including microbial communities and environmental conditions. ...
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The Khatyspyt Lagerstätte (~544 Ma, Russia) provides a valuable window into late Ediacaran Avalon‐type ecosystems with rangeomorphs, arboreomorphs, and mega‐algae. Here, we tackle the geobiology of this Lagerstätte by the combined analysis of paleontological features, sedimentary facies, and lipid biomarkers. The Khatyspyt Formation was deposited in carbonate ramp environments. Organic matter (0.12–2.22 wt.% TOC) displays characteristic Ediacaran biomarker features (e.g., eukaryotic steranes dominated by the C29 stigmastane). Some samples contain a putative 2‐methylgammacerane that was likely sourced by ciliates and/or bacteria. 24‐isopropylcholestane and 26‐methylstigmastane are consistently scarce (≤0.4% and ≤0.2% of ∑C27‐30 regular steranes, respectively). Thus, Avalon‐type organisms occupied different niches than organisms capable of directly synthesizing C30 sterane precursors among their major lipids. Relative abundances of eukaryotic steranes and bacterial hopanes (sterane/hopane ratios = 0.07–0.30) demonstrate oligotrophic and bacterially dominated marine environments, similar to findings from other successions with Ediacara‐type fossils. Ediacara‐type fossils occur in facies characterized by microbial mats and biomarkers indicative for a stratified marine environment with normal–moderate salinities (moderate–high gammacerane index of 2.3–5.7; low C35 homohopane index of 0.1–0.2). Mega‐algae, in contrast, are abundant in facies that almost entirely consist of allochthonous event layers. Biomarkers in these samples indicate a non‐stratified marine environment and normal salinities (low gammacerane index of 0.6–0.8; low C35 homohopane index of 0.1). Vertical burrowers occur in similar facies but with biomarker evidence for stratification in the water column or around the seafloor (high gammacerane index of 5.6). Thus, the distribution of macro‐organisms and burrowers was controlled by various, dynamically changing environmental factors. It appears likely that dynamic settings like the Khatyspyt Lagerstätte provided metabolic challenges for sustenance and growth which primed eukaryotic organisms to cope with changing environmental habitats, allowing for a later diversification and expansion of complex macroscopic life in the marine realm.
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We have investigated the morphology of Phyllozoon hanseni Jenkins and Gehling, a frond-like fossil organism with glide reflection symmetry from the Ediacaran of the Flinders Ranges, South Australia. The focus of this study was to measure some basic physical parameters of these fossils to identify some distinguishing trends, to help build a picture of the functional morphology of P. hanseni, and then to reconcile this information in a palaeobiological context. The main findings are that specimen length displayed a non-normal, negatively skewed distribution, and that P. hanseni possesses two distinct ends. One dubbed here the 'spoon', is rounded in profile, with steep-angled positioning of thicker units and a rosebud-like appearance at the terminus , found to always begin on the left bank of the positive hyporelief. The other end, the 'knife', displays instead a gradual decrease in both unit width and length with positioning of units perpendicular to the body axis. The area between these two sections, with sub-parallel edges, is referred to as the 'trunk'. Specimen length was found to be positively associated with both unit number and specimen width. Additionally, the findings suggest a longitudinally asymmetrical growth pattern of increasing size and number of units, with serial addition of units at the knife terminus. The observed morphology of P. hanseni suggests a lifestyle as a benthic, prostrate organism.
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For almost 150 years, megascopic structures in siliciclastic sequences of terminal Precambrian age have been frustratingly difficult to characterize and classify. As with all other areas of human knowledge, progress with exploration, documentation and understanding is growing at an exponential rate. Nevertheless, there is much to be learned from following the evolution of the logic behind the biological interpretations of these enigmatic fossils. Here, I review the history of discovery as well as some long-established core members of widely recognized clades that are still difficult to graft on to the tree of life. These ‘orphan plesions’ occupy roles that were once held by famous former Problematica, such as archaeocyaths, graptolites and rudist bivalves. In some of those cases, taxonomic enlightenment was brought about by the discovery of new characters; in others it required a better knowledge of their living counterparts. Can we use these approaches to rescue the Ediacaran orphans? Five taxa that are examined in this context are Arborea (Arboreomorpha), Dickinsonia (Dickinsoniomorpha), Pteridinium plus Ernietta (Erniettomorpha) and Kimberella (Bilateria?). With the possible exception of Dickinsonia , all of these organisms may be coelenterate grade eumetazoans.
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